ehea: using wait queues instead of msleep on ehea_flush_sq

This patch just remove a msleep loop and change to wait queue,
making the code cleaner.

Signed-off-by: Breno Leitao <leitao@linux.vnet.ibm.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>